Jay pointed out that Ekkremes offers an opportunity to explore monocolored play. Colorless mana bonuses, Operate artifacts, and monocolor hybird support monocolor decks in limited while showcasing the anti-magic group on Ekkremes.
<color> burst provides another incentive for monocolor, while also serving as a potential marquee mechanic for the denizens of Ekkremes who have embraced mana and magic.

Fire Box {2/R}
Artifact
Red Burst (~ enters the battlefield with a charge counter for each red mana spent to cast it.)
At the beginning of your upkeep, put a charge counter on this.
T, sacrifice ~: ~ deals damage to target creature equal to the number of charge counters on it.

The way monocolor was supported in shadowmoor seemed to work well, with a few cards like Corrupt and Drove of Elves, and the flexibility of hybrid making it possible to get enough playables in draft. That said, I believe Wizards has talked about how forcing monocolor too hard can be a mistake— limited needs a variety of viable decks so it doesn't get stale, and the game already pushes monocolor naturally with the mana system.

Monocolor hybrid and Burst should reward you for being deep in a color, but playable as a splash card. Fire Box might be better in that regard than Nature Elemental, which is somewhat underwhelming outside of monogreen.

Having a whole keyword devoted to monocolor play just doesn't make sense to me; Corrupt and Drove of Elves were uncommons. I mean, there's Chroma, but Chroma was pretty lame and not really a mechanical theme worth building around.